By common design, a variable vane device contains a plurality of rotatable vanes, which are arranged in an annular array. An outer shroud member circumscribes the annular array of rotatable vanes, which, in turn, circumscribes an inner hub member. Collectively, the outer shroud member and the inner hub member define a static flow assembly through which an annular flow passage extends. The rotatable vanes are positioned within this annular flow passage and can be turned about individual rotation axes to adjust the flow rate through the flow passage. Variable vane devices of this type are commonly integrated into Gas Turbine Engines (GTEs). For example, a GTE platform may be equipped with an Inlet Guide Vane (IGV) system, which contains a variable vane device positioned immediately upstream of the GTE's compressor section. Additionally or alternatively, one or more variable vane devices may be integrated into the compressor section and/or turbine section of a given GTE platform. During engine operation, an actuator rotates the vanes through an angular Range of Motion (ROM) in accordance with commands received from a controller, such as a Full Authority Digital Engine Controller (FADEC). The FADEC may command the actuator to periodically or continually adjust vane angular position in accordance with a predetermined schedule, as a function of core engine speeds, or as a function of another operational parameter of the GTE.
While capable of boosting various measures of engine performance, conventional variable vane devices remain limited in certain respects. As a primary limitation, variable vane devices are prone to leakage at the interfaces between the rotatable vanes and the surrounding static flow assembly (referred to herein as “end gap leakage”). End gap leakage is due, at least in part, to the provision of radial gaps or endwall clearances between edges of the rotatable vanes, the inner circumferential surface or endwall of the outer shroud member, and the outer circumferential surface or endwall of the inner hub member. Variable vane devices are typically designed to minimize such endwall clearances to the extent possible, while ensuring that rubbing, binding, or other physically-restrictive contact does not occur between the vane edges, the shroud endwall, and the hub endwall. However, due to the relatively complex geometric relationship between the vane edges and the annular endwalls, the endwall clearances vary dynamically in conjunction with vane rotation with a corresponding leakage penalty. Such leakage may lower GTE efficiency and result in end gap leakage flow (e.g., vortices and wakes) creating excitation forces, which can result in increased strains on rotors and other components downstream of the variable vane device.